950 
The cylinder was immersed in a cryostat, C'., consisting of a trans- 
parent vacuum glass provided with a pump stirrer (see fig. 2). Fig. 
1 shows the latter in aspect and cress section, c, is the cylinder 
and c, the piston. The temperature of the bath was regulated and 
measured by means of the gold resistance thermometer /, also shown 
in fie. 1. We may refer to earlier diagrams (Comm. No. 83, PL IV, 
and Comm. No. 127, p. 23) in which the same letters have been 
used, for details: of the arrangement Fin ¥,,, Xe, AG 44,5 ae 
)”’,. for regulating the pressure under which the liquid in the ervostat 
vaporises. 
When the temperature of the cryostat has been adjusted the same 
kind of gas as has been liquefied in it is admitted into the experi- 
mental cylinder by the tap A, through A, from the reservoir Ara. 
which has previously been filled at high pressure. A second reservoir 
Ry is coupled in parallel with 4, so that gas need be taken from 
Ry, only in sufficient quantity to complete the filling of the cylinder. 
In this way the reservoir A, is much longer available for raising 
the pressure in the experimental cylinder to the highest values. An 
other reservoir Mè, served as a regulator, and, as gas was added, the 
pressure was read on the manometer J/,. The tap A, was used for 
the evacuation of the apparatus and connections before the experi- 
ments began. The supply of gas was regulated by A. Behind A, a 
evlinder B is coupled in parallel with the experimental tube to serve 
as a buffer; to the inlet tube of this cylinder is coupled not only the 
experimental cylinder but also the differential manometer, J/,, to 
which we shall return presently. Through the tap AY, gas can be allowed 
to escape from the experimental cylinder and from the buffer. The 
pressure of the gas they contain can thus be kept at any desired 
constant value by means of A, and A. Regulation of the pressure 
is made according to the indications of the differential manometer, 
M,. one side of which is attached to the experimental apparatus and 
the other to a reservoir R, which is maintained at the required con- 
stant pressure and is, for that purpose, immersed in ice. To adjust 
to the desired pressure ihe differential manometer is first rendered 
inoperative by opening the tap K,. Care must be taken in admitting 
pressure to the manometer that friction does not give rise to diffe- 
rence of pressure between the parts of the apparatus it connects suf- 
ficient to cause the mercury of the differentiai manometer to be 
blown over. Two steel overflow vessels J/,,, M,,, serve as a safety 
device. The pressure in the experimental cylinder is read from the 
manometer J/,, which is connected to A,. A, is a safety valve which 
comes into operation when A, must be used for exhausting. 
5 
